JpetStore中MVC机制实现的研究,BeanAction以及BaseBean工作机制(看完有种恍然大悟的感觉啊!)

以前学习iBATIS时候只是粗略的看了一下代码,今天翻出来从新看了看,才发现iBATIS给的JpetStore中关于iBATIS的实现简直太精妙了,它直接把action和actionform合并在一起~ very good!!!

JpetStore的src文件夹,并无一个具体的Action,那么它是如何来完成普通Struts的Action工作了?
查看JpetStore的struts-config.xml可以发现,它的Action只有一个,即 “org.apache.stuts.beanaction.Beanaction”。通过Eclipse查看直接跳转到beanaction.jar的源代码,可以发现Beanaction继承了普通Action,即具备普通的action的功能。那么它具体Action的奥妙在哪,继续研究BeanAction的代码,发现BeanAction其实只有一个方法,源代码如下:
public final ActionForward execute(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws Exception {
    String forward = SUCCESS_FORWARD;
    try {
      if (!(form instanceof BaseBean)) {
        if (form != null) {
          throw new BeanActionException("The form for mapping '" + mapping.getPath() + "' named '" + mapping.getName() + "' was not an instance of BaseBean.  BeanAction requires an BaseBean instance.");
        } else {
          throw new BeanActionException("The form for mapping '" + mapping.getPath() + "' named '" + mapping.getName() + "' was null.  BeanAction requires an BaseBean instance.");
        }
      }
      BaseBean bean = (BaseBean) form;
      ActionContext.initCurrentContext(request, response);
      if (bean != null) {
        // Explicit Method Mapping

        Method method = null;
        String methodName = mapping.getParameter();
        if (methodName != null && !NO_METHOD_CALL.equals(methodName)) {
          try {
            method = bean.getClass().getMethod(methodName, null);
            synchronized (bean) {
              forward = bean.getInterceptor().intercept(new ActionInvoker(bean, method));
            }
          } catch (Exception e) {
            throw new BeanActionException("Error dispatching bean action via method parameter ('" + methodName + "').  Cause: " + e, e);
          }
        }



        // Path Based Method Mapping

        if (method == null && !NO_METHOD_CALL.equals(methodName)) {
          methodName = mapping.getPath();
          if (methodName.length() > 1) {
            int slash = methodName.lastIndexOf("/") + 1;
            methodName = methodName.substring(slash);
            if (methodName.length() > 0) {
              try {
                method = bean.getClass().getMethod(methodName, null);
                synchronized (bean) {
                  forward = bean.getInterceptor().intercept(new ActionInvoker(bean, method));
                }
              } catch (Exception e) {
                throw new BeanActionException("Error dispatching bean action via URL pattern ('" + methodName + "').  Cause: " + e, e);
              }
            }
          }
        }
      }
    } catch (Exception e) {
      forward = "error";
      request.setAttribute("BeanActionException", e);
    }
    return mapping.findForward(forward);
  }


最关键的地方应该就是这里:
/*通过反射,根据得到的方法名称取得方法的句柄*/ 
            method = bean.getClass().getMethod(methodName, null); 
            synchronized (bean) { 
/*下面是关键一句,调用basebean拥有的接口ActionInterceptor的实现DefaultActionInterceptor,来完成具体方法的调用*/ 
              forward = bean.getInterceptor().intercept(new ActionInvoker(bean, method)); 
            } 

而ActionInvoker中
public String invoke() {
    try {
      return (String) method.invoke(bean, null);
    } catch (Exception e) {
      throw new BeanActionException("Error invoking Action.  Cause: " + e, e);
    }
  }

至此可知,它调用的是formbean中的函数。且从这段代码可知,formbean的这类特殊函数,此处称为action方法,要符合两个特征:1)无参数;2)返回值为string,此返回string即是struts-config.xml的全局或局部的forward。



高手估计会不屑一顾,但是新手们绝对有用,还有不懂的可以看iBATIS实战中的第14章,非常经典http://book.csdn.net/bookfiles/700/
这个网站有免费试读。

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